How Is Psoriatic Arthritis Diagnosed – Or Misdiagnosed?

Diagnosing psoriatic arthritis isn’t easy. Here are some tips to help you help your doctor get it right.

By Bill Sanders

If there is little or no joint swelling, osteoarthritis is the most likely diagnosis. Swelling is a symptom most commonly seen with inflammatory forms of arthritis such as psoriatic arthritis, RA and gout. OA, which results from cartilage deterioration, does not usually involve visible or significant inflammation.

If swelling involves the full length of the fingers or toes, think PsA. This condition is called dactylitis, or “sausage fingers.” RA tends to cause swelling over individual joints.

If the affected joints are asymmetrical – in other words if a joint affected on one side of the body isn’t affected on the other side –it’s more likely to be psoriatic arthritis than rheumatoid arthritis. RA is typically symmetrical.

If joint pain is worse for more than a few minutes in the morning, or after inactivity, consider RA or PsA. With osteoarthritis, pain tends to come after activity; gout comes on rapidly, with intense pain. “If the joint pain or stiffness in the morning goes away after five minutes, then no, I wouldn’t think it’s RA or PsA necessarily. But if it lasts longer than 20 or 30 minutes, I would consider RA or PsA. Osteoarthritis in the morning is usually very brief,” Dr. Matteson says.

If blood tests show you are positive for rheumatoid factor, or RF, an autoantibody, suspect RA first. People with PsA are almost always RF-negative. “But there are a few patients who have a very low RF-factor who do not have RA and will not get it,” Dr. Matteson says. RA can develop in people who are RF-positive or -negative.

Diagnosing arthritis can be tricky, with symptoms coming and going and so many types to consider and eventually rule out – including those with similar symptoms like psoriatic arthritis, rheumatoid arthritis, osteoarthritis and gout. That’s why people sometimes are initially misdiagnosed and told they have one form of arthritis only to find out later they have another kind entirely.

“Early diagnosis is important because the window of opportunity for eliminating long-term joint problems is in the first couple of months of noticing the joint arthritis,” Dr. Matteson says. “Treating it in this timeframe, we can make a major impact on disability from joint damage. We say the first month is critical, but certainly treatment in that first three months is important.”

Even though psoriatic arthritis, or PsA, is an inflammatory form of arthritis, it is sometimes confused with osteoarthritis, or OA, which is not. It also can be mistaken for other forms of inflammatory arthritis, such as rheumatoid arthritis (RA), or gout. Below are some tips to help avoid a psoriatic arthritis misdiagnosis. Another way to make sure you get a proper diagnosis is to see a rheumatologist – a doctor trained in working with arthritis and related conditions.

If you have joint pain, and then develop the red, flaky skin that signals psoriasis, along with nail pitting, don’t rule out PsA. Psoriasis usually manifests before psoriatic arthritis symptoms, but not always and sometimes never.

If you have psoriasis symptoms and nail pitting first, and then develop joint pain, PsA is likely the culprit, particularly if there is joint swelling. But you can have psoriasis and a form of arthritis that isn’t PsA. “It also depends on your age,” Dr. Matteson says. “If the patient is 60 or 70, I’d think OA first if there isn’t swelling.”

If a single joint becomes swollen and extremely painful almost overnight, it’s probably gout. Unlike psoriatic arthritis, there is a surefire way to diagnose gout – examine joint fluid under a microscope. Uric acid crystals signal gout, which develops when the body can’t process uric acid, or produces too much. “You don’t find them in any other condition other than gout, and they are always present in gout,” Dr. Matteson says.

If there is little or no joint swelling, osteoarthritis is the most likely diagnosis. Swelling is a symptom most commonly seen with inflammatory forms of arthritis such as psoriatic arthritis, RA and gout. OA, which results from cartilage deterioration, does not usually involve visible or significant inflammation.

If swelling involves the full length of the fingers or toes, think PsA. This condition is called dactylitis, or “sausage fingers.” RA tends to cause swelling over individual joints.

If the affected joints are asymmetrical – in other words if a joint affected on one side of the body isn’t affected on the other side –it’s more likely to be psoriatic arthritis than rheumatoid arthritis. RA is typically symmetrical.

If joint pain is worse for more than a few minutes in the morning, or after inactivity, consider RA or PsA. With osteoarthritis, pain tends to come after activity; gout comes on rapidly, with intense pain. “If the joint pain or stiffness in the morning goes away after five minutes, then no, I wouldn’t think it’s RA or PsA necessarily. But if it lasts longer than 20 or 30 minutes, I would consider RA or PsA. Osteoarthritis in the morning is usually very brief,” Dr. Matteson says.

If blood tests show you are positive for rheumatoid factor, or RF, an autoantibody, suspect RA first. People with PsA are almost always RF-negative. “But there are a few patients who have a very low RF-factor who do not have RA and will not get it,” Dr. Matteson says. RA can develop in people who are RF-positive or -negative.